Re: [PATCH v3 05/14] mm, printk: introduce new format string for flags

[Michal Hocko]

On Fri 18-12-15 10:03:17, Vlastimil Babka wrote:
> In mm we use several kinds of flags bitfields that are sometimes printed for
> debugging purposes, or exported to userspace via sysfs. To make them easier to
> interpret independently on kernel version and config, we want to dump also the
> symbolic flag names. So far this has been done with repeated calls to
> pr_cont(), which is unreliable on SMP, and not usable for e.g. sysfs export.
> 
> To get a more reliable and universal solution, this patch extends printk()
> format string for pointers to handle the page flags (%pgp), gfp_flags (%pgg)
> and vma flags (%pgv). Existing users of dump_flag_names() are converted and
> simplified.
> 
> It would be possible to pass flags by value instead of pointer, but the %p
> format string for pointers already has extensions for various kernel
> structures, so it's a good fit, and the extra indirection in a non-critical
> path is negligible.
> 
> [linux@xxxxxxxxxxxxxxxxxx: lots of good implementation suggestions]
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
> Cc: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxx>

With my limitted familiarity of the printk code this looks reasonable.
Acked-by: Michal Hocko <mhocko@xxxxxxxx>

> ---
>  Documentation/printk-formats.txt | 18 ++++++++++
>  include/linux/mmdebug.h          |  6 ++++
>  lib/test_printf.c                | 53 ++++++++++++++++++++++++++++
>  lib/vsprintf.c                   | 75 ++++++++++++++++++++++++++++++++++++++++
>  mm/debug.c                       | 34 ++++++++++--------
>  mm/internal.h                    |  6 ++++
>  6 files changed, 178 insertions(+), 14 deletions(-)
> 
> diff --git a/Documentation/printk-formats.txt b/Documentation/printk-formats.txt
> index 602fee945d1d..e878e99ad686 100644
> --- a/Documentation/printk-formats.txt
> +++ b/Documentation/printk-formats.txt
> @@ -292,6 +292,24 @@ Raw pointer value SHOULD be printed with %p. The kernel supports
>  
>  	Passed by reference.
>  
> +Flags bitfields such as page flags, gfp_flags:
> +
> +	%pgp	referenced|uptodate|lru|active|private
> +	%pgg	GFP_USER|GFP_DMA32|GFP_NOWARN
> +	%pgv	read|exec|mayread|maywrite|mayexec|denywrite
> +
> +	For printing flags bitfields as a collection of symbolic constants that
> +	would construct the value. The type of flags is given by the third
> +	character. Currently supported are [p]age flags, [v]ma_flags (both
> +	expect unsigned long *) and [g]fp_flags (expects gfp_t *). The flag
> +	names and print order depends on the particular	type.
> +
> +	Note that this format should not be used directly in TP_printk() part
> +	of a tracepoint. Instead, use the show_*_flags() functions from
> +	<trace/events/mmflags.h>.
> +
> +	Passed by reference.
> +
>  Network device features:
>  
>  	%pNF	0x000000000000c000
> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> index c447d8055e50..2c8286cf162e 100644
> --- a/include/linux/mmdebug.h
> +++ b/include/linux/mmdebug.h
> @@ -2,11 +2,17 @@
>  #define LINUX_MM_DEBUG_H 1
>  
>  #include <linux/stringify.h>
> +#include <linux/types.h>
> +#include <linux/tracepoint.h>
>  
>  struct page;
>  struct vm_area_struct;
>  struct mm_struct;
>  
> +extern const struct trace_print_flags pageflag_names[];
> +extern const struct trace_print_flags vmaflag_names[];
> +extern const struct trace_print_flags gfpflag_names[];
> +
>  extern void dump_page(struct page *page, const char *reason);
>  extern void dump_page_badflags(struct page *page, const char *reason,
>  			       unsigned long badflags);
> diff --git a/lib/test_printf.c b/lib/test_printf.c
> index 4f6ae60433bc..5c7c8ebf3689 100644
> --- a/lib/test_printf.c
> +++ b/lib/test_printf.c
> @@ -17,6 +17,9 @@
>  #include <linux/socket.h>
>  #include <linux/in.h>
>  
> +#include <linux/gfp.h>
> +#include <linux/mm.h>
> +
>  #define BUF_SIZE 256
>  #define PAD_SIZE 16
>  #define FILL_CHAR '$'
> @@ -411,6 +414,55 @@ netdev_features(void)
>  }
>  
>  static void __init
> +flags(void)
> +{
> +	unsigned long flags;
> +	gfp_t gfp;
> +	char *cmp_buffer;
> +
> +	flags = 0;
> +	test("", "%pgp", &flags);
> +
> +	/* Page flags should filter the zone id */
> +	flags = 1UL << NR_PAGEFLAGS;
> +	test("", "%pgp", &flags);
> +
> +	flags |= 1UL << PG_uptodate | 1UL << PG_dirty | 1UL << PG_lru
> +		| 1UL << PG_active | 1UL << PG_swapbacked;
> +	test("uptodate|dirty|lru|active|swapbacked", "%pgp", &flags);
> +
> +
> +	flags = VM_READ | VM_EXEC | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC
> +			| VM_DENYWRITE;
> +	test("read|exec|mayread|maywrite|mayexec|denywrite", "%pgv", &flags);
> +
> +	gfp = GFP_TRANSHUGE;
> +	test("GFP_TRANSHUGE", "%pgg", &gfp);
> +
> +	gfp = GFP_ATOMIC|__GFP_DMA;
> +	test("GFP_ATOMIC|GFP_DMA", "%pgg", &gfp);
> +
> +	gfp = __GFP_ATOMIC;
> +	test("__GFP_ATOMIC", "%pgg", &gfp);
> +
> +	cmp_buffer = kmalloc(BUF_SIZE, GFP_KERNEL);
> +	if (!cmp_buffer)
> +		return;
> +
> +	/* Any flags not translated by the table should remain numeric */
> +	gfp = ~__GFP_BITS_MASK;
> +	snprintf(cmp_buffer, BUF_SIZE, "%#lx", (unsigned long) gfp);
> +	test(cmp_buffer, "%pgg", &gfp);
> +
> +	snprintf(cmp_buffer, BUF_SIZE, "__GFP_ATOMIC|%#lx",
> +							(unsigned long) gfp);
> +	gfp |= __GFP_ATOMIC;
> +	test(cmp_buffer, "%pgg", &gfp);
> +
> +	kfree(cmp_buffer);
> +}
> +
> +static void __init
>  test_pointer(void)
>  {
>  	plain();
> @@ -428,6 +480,7 @@ test_pointer(void)
>  	struct_clk();
>  	bitmap();
>  	netdev_features();
> +	flags();
>  }
>  
>  static int __init
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index cf064b17c50c..a254973d005d 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -32,6 +32,8 @@
>  #include <linux/cred.h>
>  #include <net/addrconf.h>
>  
> +#include "../mm/internal.h"	/* For the trace_print_flags arrays */
> +
>  #include <asm/page.h>		/* for PAGE_SIZE */
>  #include <asm/sections.h>	/* for dereference_function_descriptor() */
>  #include <asm/byteorder.h>	/* cpu_to_le16 */
> @@ -1372,6 +1374,72 @@ char *clock(char *buf, char *end, struct clk *clk, struct printf_spec spec,
>  	}
>  }
>  
> +static
> +char *format_flags(char *buf, char *end, unsigned long flags,
> +					const struct trace_print_flags *names)
> +{
> +	unsigned long mask;
> +	const struct printf_spec strspec = {
> +		.field_width = -1,
> +		.precision = -1,
> +	};
> +	const struct printf_spec numspec = {
> +		.flags = SPECIAL|SMALL,
> +		.field_width = -1,
> +		.precision = -1,
> +		.base = 16,
> +	};
> +
> +	for ( ; flags && names->name; names++) {
> +		mask = names->mask;
> +		if ((flags & mask) != mask)
> +			continue;
> +
> +		buf = string(buf, end, names->name, strspec);
> +
> +		flags &= ~mask;
> +		if (flags) {
> +			if (buf < end)
> +				*buf = '|';
> +			buf++;
> +		}
> +	}
> +
> +	if (flags)
> +		buf = number(buf, end, flags, numspec);
> +
> +	return buf;
> +}
> +
> +static noinline_for_stack
> +char *flags_string(char *buf, char *end, void *flags_ptr, const char *fmt)
> +{
> +	unsigned long flags;
> +	const struct trace_print_flags *names;
> +
> +	switch (fmt[1]) {
> +	case 'p':
> +		flags = *(unsigned long *)flags_ptr;
> +		/* Remove zone id */
> +		flags &= (1UL << NR_PAGEFLAGS) - 1;
> +		names = pageflag_names;
> +		break;
> +	case 'v':
> +		flags = *(unsigned long *)flags_ptr;
> +		names = vmaflag_names;
> +		break;
> +	case 'g':
> +		flags = *(gfp_t *)flags_ptr;
> +		names = gfpflag_names;
> +		break;
> +	default:
> +		WARN_ONCE(1, "Unsupported flags modifier: %c\n", fmt[1]);
> +		return buf;
> +	}
> +
> +	return format_flags(buf, end, flags, names);
> +}
> +
>  int kptr_restrict __read_mostly;
>  
>  /*
> @@ -1459,6 +1527,11 @@ int kptr_restrict __read_mostly;
>   * - 'Cn' For a clock, it prints the name (Common Clock Framework) or address
>   *        (legacy clock framework) of the clock
>   * - 'Cr' For a clock, it prints the current rate of the clock
> + * - 'g' For flags to be printed as a collection of symbolic strings that would
> + *       construct the specific value. Supported flags given by option:
> + *       p page flags (see struct page) given as pointer to unsigned long
> + *       g gfp flags (GFP_* and __GFP_*) given as pointer to gfp_t
> + *       v vma flags (VM_*) given as pointer to unsigned long
>   *
>   * ** Please update also Documentation/printk-formats.txt when making changes **
>   *
> @@ -1611,6 +1684,8 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
>  		return dentry_name(buf, end,
>  				   ((const struct file *)ptr)->f_path.dentry,
>  				   spec, fmt);
> +	case 'g':
> +		return flags_string(buf, end, ptr, fmt);
>  	}
>  	spec.flags |= SMALL;
>  	if (spec.field_width == -1) {
> diff --git a/mm/debug.c b/mm/debug.c
> index 85f71e4ce59f..79621a5ce46f 100644
> --- a/mm/debug.c
> +++ b/mm/debug.c
> @@ -11,12 +11,21 @@
>  #include <linux/memcontrol.h>
>  #include <trace/events/mmflags.h>
>  
> -static const struct trace_print_flags pageflag_names[] = {
> -	__def_pageflag_names
> +#include "internal.h"
> +
> +const struct trace_print_flags pageflag_names[] = {
> +	__def_pageflag_names,
> +	{0, NULL}
> +};
> +
> +const struct trace_print_flags gfpflag_names[] = {
> +	__def_gfpflag_names,
> +	{0, NULL}
>  };
>  
> -static const struct trace_print_flags gfpflag_names[] = {
> -	__def_gfpflag_names
> +const struct trace_print_flags vmaflag_names[] = {
> +	__def_vmaflag_names,
> +	{0, NULL}
>  };
>  
>  static void dump_flags(unsigned long flags,
> @@ -58,14 +67,15 @@ void dump_page_badflags(struct page *page, const char *reason,
>  	if (PageCompound(page))
>  		pr_cont(" compound_mapcount: %d", compound_mapcount(page));
>  	pr_cont("\n");
> -	BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS);
> -	dump_flags(page->flags, pageflag_names, ARRAY_SIZE(pageflag_names));
> +	BUILD_BUG_ON(ARRAY_SIZE(pageflag_names) != __NR_PAGEFLAGS + 1);
> +	dump_flags(page->flags, pageflag_names,
> +					ARRAY_SIZE(pageflag_names) - 1);
>  	if (reason)
>  		pr_alert("page dumped because: %s\n", reason);
>  	if (page->flags & badflags) {
>  		pr_alert("bad because of flags:\n");
> -		dump_flags(page->flags & badflags,
> -				pageflag_names, ARRAY_SIZE(pageflag_names));
> +		dump_flags(page->flags & badflags, pageflag_names,
> +					ARRAY_SIZE(pageflag_names) - 1);
>  	}
>  #ifdef CONFIG_MEMCG
>  	if (page->mem_cgroup)
> @@ -81,10 +91,6 @@ EXPORT_SYMBOL(dump_page);
>  
>  #ifdef CONFIG_DEBUG_VM
>  
> -static const struct trace_print_flags vmaflag_names[] = {
> -	__def_vmaflag_names
> -};
> -
>  void dump_vma(const struct vm_area_struct *vma)
>  {
>  	pr_emerg("vma %p start %p end %p\n"
> @@ -96,7 +102,7 @@ void dump_vma(const struct vm_area_struct *vma)
>  		(unsigned long)pgprot_val(vma->vm_page_prot),
>  		vma->anon_vma, vma->vm_ops, vma->vm_pgoff,
>  		vma->vm_file, vma->vm_private_data);
> -	dump_flags(vma->vm_flags, vmaflag_names, ARRAY_SIZE(vmaflag_names));
> +	dump_flags(vma->vm_flags, vmaflag_names, ARRAY_SIZE(vmaflag_names) - 1);
>  }
>  EXPORT_SYMBOL(dump_vma);
>  
> @@ -168,7 +174,7 @@ void dump_mm(const struct mm_struct *mm)
>  		);
>  
>  		dump_flags(mm->def_flags, vmaflag_names,
> -				ARRAY_SIZE(vmaflag_names));
> +				ARRAY_SIZE(vmaflag_names) - 1);
>  }
>  
>  #endif		/* CONFIG_DEBUG_VM */
> diff --git a/mm/internal.h b/mm/internal.h
> index d01a41c00bec..8d2f8e3fd7d8 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -14,6 +14,7 @@
>  #include <linux/fs.h>
>  #include <linux/mm.h>
>  #include <linux/pagemap.h>
> +#include <linux/tracepoint-defs.h>
>  
>  /*
>   * The set of flags that only affect watermark checking and reclaim
> @@ -441,4 +442,9 @@ static inline void try_to_unmap_flush_dirty(void)
>  }
>  
>  #endif /* CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH */
> +
> +extern const struct trace_print_flags pageflag_names[];
> +extern const struct trace_print_flags vmaflag_names[];
> +extern const struct trace_print_flags gfpflag_names[];
> +
>  #endif	/* __MM_INTERNAL_H */
> -- 
> 2.6.3

-- 
Michal Hocko
SUSE Labs
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